The present invention relates to a fuel injection system, and more particularly to a fuel injection system for spark plug-ignited internal combustion engines with compression of the air-fuel mixture, including a continuously delivering fuel pump, a fuel injection quantity regulation operating in dependence on the air quantity streaming through the suction tube of the engine, a pressure regulator for determining the normal system pressure of the installation, and injection nozzles, whose opening pressure is lower than the system pressure.
In the use of a fuel injection system of this type, difficulties can occur after shut off of the hot engine, because the subsequent high heat of the engine, which remains as a result of the lack of circulated coolant (cooling air, cooling water), can have one or both of the following effects:
1. A PORTION OF THE FUEL CONTAINED IN THE INJECTION SYSTEM, AND ESPECIALLY BETWEEN THE FUEL METERING LOCATION AND THE INJECTION LOCATION, IS VAPORIZED. This leads to fuel shrinkage and therefore to a shortage of fuel for engine starting after the engine has cooled off; and
2. DURING THE COOLING OFF OF THE FUEL, THE VOLUME SHRINKAGE RESULTS IN REDUCING THE PRESSURE IN THE CLOSED SYSTEM AND ELEMENTS, WHICH OPERATE IN DEPENDENCE ON THE PRESSURE AS DOES, FOR EXAMPLE, A FUEL METERING VALVE. This causes a displacement of such a valve into a position in which the air-fuel mixture supplied is too rich so that the engine floods during start up.
To these two can be added a third adverse effect resulting from a volume reduction of fuel caused by leakages which are always present. This volume reduction can lead to starting difficulties even when the engine is started hot.